1. Field of the Invention
The present invention relates to a sheet feeder and an image forming apparatus, and more particularly to a sheet feeder configured to blow air to float a sheet from a stack of sheets, to pick up the sheet and to feed the sheet into a sheet path, and an image forming apparatus comprising the sheet feeder.
2. Description of Related Art
A sheet feeder disclosed in Japanese Patent Laid-Open Publication No. 2010-254462 is well known as an example of sheet feeders of an air-blowing type that blows air to float a sheet from a stack of sheets, picks up the sheet and feeds the sheet into a sheet path. In a conventional sheet feeder of this type, one or more sheets are floated by an air blower, and a picture of the topmost sheet and the second topmost sheet of the floated sheets is taken. Then, the distance between the topmost sheet and the second topmost sheet is determined, and the air volume blown from the air blower is controlled based on the determined distance.
In such a conventional sheet feeder, however, there is a risk of not perceiving the exact positions of the floated sheets. The sheets floated by the air blower move up and down repeatedly at a high speed, and the floated sheets cannot be always be photographed when they are at the highest positions. This causes a problem that, in some instances, what has been determined is not the distance between the topmost sheet and the second topmost sheet but the distance between two adjacent sheets at the middle level of the floated sheets.